#!/usr/bin/env python
# coding: utf-8

# This notebook was prepared by [Donne Martin](https://github.com/donnemartin). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges).

# # Challenge Notebook

# ## Problem: Find the length of the longest substring with at most k distinct characters.
# 
# * [Constraints](#Constraints)
# * [Test Cases](#Test-Cases)
# * [Algorithm](#Algorithm)
# * [Code](#Code)
# * [Unit Test](#Unit-Test)
# * [Solution Notebook](#Solution-Notebook)

# ## Constraints
# 
# * Can we assume the inputs are valid?
#     * No
# * Can we assume the strings are ASCII?
#     * Yes
# * Is this case sensitive?
#     * Yes
# * Is a substring a contiguous block of chars?
#     * Yes
# * Do we expect an int as a result?
#     * Yes
# * Can we assume this fits memory?
#     * Yes

# ## Test Cases
# 
# * None -> TypeError
# * '', k = 3 -> 0
# * 'abcabcdefgghiij', k=3 -> 6
# * 'abcabcdefgghighij', k=3 -> 7

# ## Algorithm
# 
# Refer to the [Solution Notebook]().  If you are stuck and need a hint, the solution notebook's algorithm discussion might be a good place to start.

# ## Code

# In[ ]:


class Solution(object):

    def longest_substr(self, string, k):
        # TODO: Implement me
        pass


# ## Unit Test

# **The following unit test is expected to fail until you solve the challenge.**

# In[ ]:


# %load test_longest_substr.py
import unittest


class TestSolution(unittest.TestCase):

    def test_longest_substr(self):
        solution = Solution()
        self.assertRaises(TypeError, solution.longest_substr, None)
        self.assertEqual(solution.longest_substr('', k=3), 0)
        self.assertEqual(solution.longest_substr('abcabcdefgghiij', k=3), 6)
        self.assertEqual(solution.longest_substr('abcabcdefgghighij', k=3), 7)
        print('Success: test_longest_substr')


def main():
    test = TestSolution()
    test.test_longest_substr()


if __name__ == '__main__':
    main()


# ## Solution Notebook
# 
# Review the [Solution Notebook]() for a discussion on algorithms and code solutions.